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Abstract:

A wireless moving image transmission terminal for encoding and wirelessly
transmitting data comprises a moving image acquisition unit for acquiring
data to be reproduced in time sequence, an encoder for encoding the data
acquired in the moving image acquisition unit by inter-frame predictive
encoding in units of frame and generating encoded data, a wireless
transmission/reception unit for wirelessly transmitting the encoded data,
a wireless state determination unit for determining a wireless state of
the wireless transmission/reception unit, and when determining that the
wireless state is deteriorated, interrupting transmission of the encoded
data by the wireless transmission/reception unit, and a referenced frame
designation unit for, when the wireless state determination unit
interrupts transmission of the encoded data by the wireless
transmission/reception unit , designating a referenced frame for
inter-frame predictive encoding in the encoder.

Claims:

1-17. (canceled)

18. A wireless transmission terminal for encoding and wirelessly
transmitting moving image data, comprising: a data acquisition unit for
shooting an object and acquiring the moving image data; an encoder for
encoding the data acquired in the data acquisition unit by inter-frame
predictive encoding in units of frame and generating encoded data; a
wireless transmission unit for wirelessly transmitting the encoded data;
a wireless transmission control unit for, when determining that a
wireless state is deteriorated based on a reduction in a reception
intensity or start of handover, interrupting transmission of the encoded
data by the wireless transmission unit; and a referenced frame
designation unit for designating, as a referenced frame for the
inter-frame predictive encoding in the encoder, the latest frame which is
decodable by frames transmitted before the wireless transmission control
unit interrupts transmission of the encoded data by the wireless
transmission unit.

19. The wireless transmission terminal according to claim 18, comprising
a buffer for storing the encoded data to be transmitted by the wireless
transmission unit while the wireless transmission control unit interrupts
transmission of the encoded data by the wireless transmission unit.

20. The wireless transmission terminal according to claim 18, wherein
after the wireless transmission control unit determines that the wireless
state is recovered, the wireless transmission unit transmits the encoded
data stored in the buffer.

21. The wireless transmission terminal according to claim 18, wherein
after the wireless transmission control unit determines that the wireless
state is recovered, the referenced frame designation unit cancels the
designation of the referenced frame.

22. The wireless transmission terminal according to claim 21, wherein
after the wireless transmission control unit determines that the wireless
state is recovered, and a predetermined number of frames are encoded
using the designated referenced frame, the referenced frame designation
unit cancels the designation of the referenced frame.

23. The wireless transmission terminal according to claim 19, wherein
when receiving the encoded data exceeding a capacity of the buffer, the
buffer discards the stored encoded data in units of frame.

24. The wireless transmission terminal according to claim 23, wherein the
buffer discards the stored encoded data sequentially from the oldest
data.

25. The wireless transmission terminal according to claim 23, wherein the
buffer discards the stored encoded data at predetermined frame intervals
sequentially from the oldest data.

26. The wireless transmission terminal according to claim 18, wherein
until handover is completed after the wireless transmission terminal
starts the handover, the wireless transmission control unit interrupts
transmission of the encoded data by the wireless transmission unit.

27. An encoding device used for a wireless transmission terminal
comprising a data acquisition unit for shooting an object and acquiring
moving image data, a wireless transmission unit for encoding the moving
image data by inter-frame predictive encoding in units of frame and
wirelessly transmitting the encoded data, and a wireless transmission
control unit for, when determining that a wireless state is deteriorated
based on a reduction in a reception intensity or start of handover,
interrupting transmission of the encoded data by the wireless
transmission unit, the encoding device comprising: an encoder for
encoding the data acquired by the data acquisition unit by inter-frame
predictive encoding in units of frame and generating the encoded data;
and a referenced frame designation unit for designating, as a referenced
frame for the inter-frame predictive encoding in the encoder, the latest
frame which is decodable by frames transmitted before the wireless
transmission control unit interrupts transmission of the encoded data by
the wireless transmission unit.

28. A wireless transmission method for encoding and wirelessly
transmitting moving image data, comprising: a data acquisition step of
shooting an object and acquiring moving image data; an encoding step of
encoding the data acquired in the data acquisition step by inter-frame
predictive encoding in units of frame and generating encoded data; a
wireless transmission step of wirelessly transmitting the encoded data; a
wireless transmission control step of, when determining that a wireless
state is deteriorated based on a reduction in a reception intensity or
start of handover, interrupting transmission of the encoded data; and a
referenced frame designation step of designating, as a referenced frame
for the inter-frame predictive encoding in the encoder, the latest frame
which is decodable by frames transmitted before the wireless transmission
control step interrupts transmission of the encoded data.

29. An encoding method performed in a wireless transmission terminal
comprising a data acquisition unit for shooting an object and acquiring
moving image data, a wireless transmission unit for encoding the moving
image data by inter-frame predictive encoding in units of frame and
wirelessly transmitting the encoded data, and a wireless transmission
control unit for, when determining that a wireless state is deteriorated
based on a reduction in a reception intensity or start of handover,
interrupting transmission of the encoded data by the wireless
transmission unit, the encoding method comprising: an encoding step of
encoding the data acquired by the data acquisition unit and to be
reproduced in time sequence by inter-frame predictive encoding in units
of frame and generating the encoded data; and a referenced frame
designation step of designating, as a referenced frame for the
inter-frame predictive encoding in the encoder, the latest frame which is
decodable by frames transmitted before the wireless transmission control
unit interrupts transmission of the encoded data by the wireless
transmission unit.

30. A computer-readable storage medium having stored therein a computer
program for causing a computer to perform the wireless transmission
method according to claim 28.

31. A computer-readable storage medium having stored therein a computer
program for causing a computer to perform the encoding method according
to claim 29.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of Patent Application
No. 2010-286447 filed on Dec. 22, 2010 in Japan, the contents of which
are incorporated herein by reference.

TECHNICAL FIELD

[0002] The present invention relates to a wireless transmission terminal
and wireless transmission method for encoding and wirelessly transmitting
data to be reproduced in time sequence by inter-frame predictive
encoding, an encoder for the wireless transmission terminal and an
encoding method for the wireless transmission method, and computer
programs for performing the methods.

BACKGROUND ART

[0003] There has been conventionally known a movable terminal having the
functions of shooting an object, generating moving image data, and
wirelessly transmitting the generated moving image data (which will be
called "wireless moving image transmission terminal" below). The wireless
moving image transmission terminals typically include digital video
cameras having a wireless communication function and capable of
wirelessly transmitting generated moving image data, or wireless
communication devices (such as cell phone) having the functions of
shooting and transmitting moving images.

[0004] It is advantageous to encode moving image data by inter-frame
predictive encoding when the moving image data is wirelessly transmitted
from the wireless moving image transmission terminal. The inter-frame
predictive encoding generates an in-frame encoding frame (I picture)
obtained by encoding an input image itself at predetermined intervals,
and generates a plurality of inter-frame encoding frames (P pictures or B
pictures) obtained by encoding a difference between the input image and a
predictive image between the I pictures, thereby remarkably compressing
moving image data. In this way, the moving image data is compressed for
transmission so that a transmission destination can receive the moving
image data without delay and can reproduce moving images shot by the
wireless moving image transmission terminal in real-time.

[0005] FIG. 3 is a configuration diagram of a wireless transmission system
for wirelessly transmitting moving image data from a wireless moving
image transmission terminal. As illustrated in FIG. 3, the wireless
transmission system is provided with a plurality of access points. In the
example of FIG. 3, the access points AP1 and AP2 are provided. The access
points each cover their own wireless areas. In the example of FIG. 3, the
access point AP1 covers a wireless area AR1 and the access point AP2
covers a wireless area AR2. As illustrated in FIG. 3, the wireless areas
may partially overlap on each other.

[0006] The wireless moving image transmission terminal establishes an
association with an access point of its belonging wireless area for
making communication. In the example of FIG. 3, a wireless moving image
transmission terminal TM1 makes communication with the access point AP1
covering the wireless area AR1, and a wireless moving image transmission
terminal TM2 makes communication with the access point AP2 covering the
wireless area AR2. The wireless moving image transmission terminals TM1
and TM2 transmit shot and generated moving image data to a monitor MT as
a transmission destination via the access points AP1 and AP2 and relay
devices RT such as a router, respectively.

[0007] When the wireless moving image transmission terminal moves, exits a
current belonging wireless area and enters a new wireless area, handover
is performed. The wireless moving image transmission terminal keeps
shooting and keeps generating moving image data even while the handover
is being performed. However, a processing of authenticating a new access
point is performed during the handover, and thus a service disconnected
period for several tens milliseconds to several seconds in which moving
image data cannot be transmitted is caused. Thereby, the transmission
destination cannot reproduce the moving images shot by the wireless
moving image transmission terminal in real-time.

[0008] FIG. 4 is a diagram for explaining a moving image data transmission
processing during handover according to a first conventional technique.
The wireless moving image transmission terminal as a transmission source
of moving image data includes an encoder for encoding the moving image
data by inter-frame predictive encoding, and a wireless
transmission/reception unit for packetizing and transmitting the encoded
moving image data. A transmission destination of moving image data
includes a reception unit for receiving the packets, and a decoder for
decoding the moving image data received in the reception unit.

[0009] When moving image data is transmitted within a wireless cell in
which the wireless moving image transmission terminal is present, the
wireless transmission/reception unit makes the moving image data encoded
by inter-frame predictive encoding in the encoder in IP packets and
wirelessly transmits the same. In the transmission destination, the
reception unit receives the same and the decoder decodes the moving image
data. In FIG. 4, moving image data of frame 1 and frame 2 is transmitted
from the wireless moving image transmission terminal to the transmission
destination and is reproduced at the transmission destination as
described above. The frames of the moving image shot in the wireless
moving image transmission terminal can be reproduced at the transmission
destination in real-time.

[0010] There is a time lag between when an object is shot by the wireless
moving image transmission terminal and its moving image data is encoded
and transmitted from the wireless moving image transmission terminal and
when it is received and decoded at the transmission destination, and
reproduction in "real-time" is that moving image data can be reproduced
only in the time lag like the frame 1 or frame 2.

[0011] When the wireless moving image transmission terminal starts
handover, the wireless moving image transmission terminal cannot transmit
moving image data as described above. Thus, in the first conventional
technique illustrated in FIG. 4, during handover, the wireless moving
image transmission terminal stores packets of generated moving image data
in a buffer, and transmits the packets stored in the buffer to a new
access point after the handover is completed. In the example of FIG. 4,
packets of the moving image data in frames 3, 4, 5 generated during
handover are stored in the buffer and are sequentially transmitted after
the handover is completed.

[0012] According to the first conventional technique, reproduction of the
frames which cannot be transmitted during handover is delayed at the
transmission destination, but all the frames can be reproduced
irrespective of interruption of data transmission due to the handover.
However, according to the first conventional technique, the wireless
moving image transmission terminal needs a buffer with a sufficient
capacity for storing moving image data generated during handover. When
the wireless moving image transmission terminal is a small portable
device such as cell phone or digital video camera, it is difficult to
secure such a buffer with a sufficient capacity.

[0013] FIG. 5 is a diagram for explaining a case in which overflow occurs
in a buffer when moving image data during handover is stored in a buffer
even when the buffer does not have a sufficient capacity. In the case of
FIG. 5, as a result of the overflow of the buffer, all the packets of the
frame 3 and part of the packets of the frame 4 are discarded. Thus, also
after handover is completed, the frame 3 cannot be reproduced in a
transmission destination, and only part of the packets of the frame 4 is
present and thus cannot be completely reproduced.

[0014] In the case of FIG. 5, the frame 3 or the frame 4 whose part of or
total packets are not transmitted cannot be reproduced, and due to a
cause described later, even the frame 5 and its subsequent frames whose
total packets are transmitted after handover is completed are
deteriorated in an image quality of the reproduced image at the
transmission destination.

[0015] As illustrated in FIG. 5, the moving image frames include I
pictures and P pictures. The I picture is an image which is a start point
of reproducing moving images and which is encoded by in-frame predictive
encoding. The P picture is a frame which is encoded by forward
inter-frame predictive encoding from a former I picture or P picture.

[0016] With reference to FIG. 5, the frame 1 and the frame 2 are
packetized and all the packets are completely transmitted to the
transmission destination. Since handover is started at the wireless
moving image transmission terminal after the frame 2 is transmitted, the
frame 3 and its subsequent frames are stored in the buffer in the service
disconnected period. However, since the buffer does not have an enough
capacity to store the packets for three frames, part of the packets of
the frame 3 is discarded when the packets of the frame 5 are stored.

[0017] The handover is completed before the frame 6 is completely encoded,
and the wireless moving image transmission terminal enters communicable
with a new access point, but the packets of the frame 6 are stored in the
buffer before the communication is restarted to transmit part of the
packets of the frame 3, and thus the packets of the frame 3 and part of
the packets of the frame 4 are discarded. Thus, when the handover is
completed and the packets are transmitted to the new access point, the
buffer stores all the packets of the frame 6 and the frame 5 and only
part of the packets of the frame 4. Therefore, even when transmission is
restarted after the handover is completed, only part of the packets of
the frame 4 can be transmitted. The packets stored in the buffer are
sequentially transmitted from the frame 5 to the frame 7 after the
handover is completed, thereby completely transmitting one frame. The
frame 8 and its subsequent frames can be transmitted as usual.

[0018] The transmission destination receives complete data for the frame 5
but needs moving image data of the frame 4 for decoding the frame 5, but
part of the packets of the frame 4 is missing and complete moving image
data cannot be obtained as described above, and thus the image quality of
the frame 5 is deteriorated.

[0019] The encoded data of the frame 6 and the frame 7 is transmitted to
the transmission destination, but the image quality of the frame 5 and
the frame 6 to be referred to is deteriorated, and thus the image quality
of the frame 6 and the frame 7 is deteriorated.

[0020] In this way, once handover is started and transmission is
interrupted, even if the handover is then completed and the transmission
is restarted, the frames cannot be normally reproduced until a next I
picture at the transmission destination. Thus, according to the first
conventional technique, it is not possible to sufficiently reduce the
frames which cannot be normally reproduced due to handover while
restricting the capacity of the buffer required for the wireless moving
image transmission terminal.

[0021] To the contrary, according to a second conventional technique
(Patent Literature 1), frames after the wireless moving image
transmission terminal starts handover are subjected to in-frame encoding
to be assumed as I pictures. According to the second conventional
technique, the frames after the handover is started are subjected to
in-frame encoding (for a certain period after the handover is completed
as needed) so that complete reproduction can be performed immediately
after the handover is completed.

[0023] According to the second conventional technique, however, since
moving image data to be stored in the buffer during handover is in-frame
encoding frames (I pictures), the number of frames capable of being
stored in the buffer is less than when moving image data is inter-frame
encoding frames (P pictures or B pictures). For example, in the example
of FIG. 5, it is assumed that the buffer does not have a capacity for
storing the I pictures for two frames. In this case, when the packets of
the frame 6 are buffered, part of or all the packets of not only the
frame 4 but also the frame 5 are discarded and the frame 5 cannot be
completely reproduced.

[0024] Thus, according to the second conventional technique, it is not
possible to sufficiently reduce the frames which cannot be normally
reproduced in a service disconnected period due to handover while
restricting the capacity of the buffer required for the wireless moving
image transmission terminal.

[0025] The present invention has been made in terms of the above problems,
and an object thereof is to provide a wireless transmission terminal
capable of reducing the number of frames which cannot be normally
reproduced in a service disconnected period (including when reproduction
cannot be completely performed, when reproduction is incomplete and when
an image quality of a reproduced image is deteriorated, but limited
thereto) while restricting a capacity of a buffer required for the
wireless transmission terminal.

Solution to Problem

[0026] In order to solve the above conventional problems, the wireless
transmission terminal according to the present invention is a wireless
transmission terminal for encoding and wirelessly transmitting data to be
reproduced in time sequence, comprising a data acquisition unit for
acquiring the data to be reproduced in time sequence, an encoder for
encoding the data acquired in the data acquisition unit by inter-frame
predictive encoding in units of frame and generating encoded data, a
wireless transmission unit for wirelessly transmitting the encoded data,
a wireless transmission control unit for determining a wireless state of
the wireless transmission unit, and when determining that the wireless
state is deteriorated, interrupting transmission of the encoded data by
the wireless transmission unit, and a referenced frame designation unit
for, when the wireless transmission control unit interrupts transmission
of the encoded data by the wireless transmission unit, designating a
referenced frame for the inter-frame predictive encoding in the encoder.

[0027] The wireless transmission terminal may further includes a buffer
for storing the encoded data to be transmitted by the wireless
transmission unit while the wireless transmission control unit interrupts
transmission of the encoded data by the wireless transmission unit.

[0028] In the wireless transmission terminal, the referenced frame
designation unit may designate, as the referenced frame, a frame
decodable among frames transmitted before the wireless transmission
control unit interrupts transmission of the encoded data by the wireless
transmission unit.

[0029] In the wireless transmission terminal, the referenced frame
designation unit may designate, as the referenced frame, the decodable
latest frame among frames transmitted before the wireless transmission
control unit interrupts transmission of the encoded data by the wireless
transmission unit.

[0030] In the wireless transmission terminal, after the wireless
transmission control unit determines that the wireless state is
recovered, the wireless transmission unit may transmit the encoded data
stored in the buffer.

[0031] In the wireless transmission terminal, after the wireless
transmission control unit determines that the wireless state is
recovered, the referenced frame designation unit may cancel designating
the referenced frame.

[0032] In the wireless transmission terminal, after the wireless
transmission control unit determines that the wireless state is
recovered, and a predetermined number of frames are encoded by the
designated referenced frame, the referenced frame designation unit may
cancel designating the referenced frame.

[0033] In the wireless transmission terminal, when receiving the encoded
data exceeding a capacity of the buffer, the buffer may discard the
stored encoded data in units of frame.

[0034] In the wireless transmission terminal, the buffer may discard the
stored encoded data sequentially from the oldest data.

[0035] In the wireless transmission terminal, the buffer may discard the
stored encoded data at predetermined frame intervals sequentially from
the oldest data.

[0036] In the wireless transmission terminal, the wireless transmission
unit may further include a reception function, and while a reception
intensity of the wireless transmission unit is equal to or less than a
predetermined threshold, the wireless transmission control unit may
interrupt transmission of the encoded data by the wireless transmission
unit.

[0037] In the wireless transmission terminal, until handover is completed
after the wireless transmission terminal starts the handover, the
wireless transmission control unit may interrupt transmission of the
encoded data by the wireless transmission unit.

[0038] Another aspect of the present invention is an encoding device used
for a wireless transmission terminal comprising a data acquisition unit
for acquiring data to be reproduced in time sequence, a wireless
transmission unit for encoding the data to be reproduced in time sequence
by inter-frame predictive encoding in units of frame and wirelessly
transmitting the encoded data, and a wireless transmission control unit
for determining a wireless state of the wireless transmission unit, and
when determining that the wireless state is deteriorated, interrupting
transmission of the encoded data by the wireless transmission unit, the
encoding device comprising an encoder for encoding the data acquired in
the data acquisition unit and reproduced in time sequence by inter-frame
predictive encoding in units of frame and generating the encoded data,
and a referenced frame designation unit for, when the wireless
transmission control unit interrupts transmission of the encoded data by
the wireless transmission unit, designating a referenced frame for the
inter-frame predictive encoding by the encoder.

[0039] Still another aspect of the present invention is a wireless
transmission method for encoding and wirelessly transmitting data to be
reproduced in time sequence, comprising a data acquisition step of
acquiring the data to be reproduced in time sequence, an encoding step of
encoding the data acquired in the data acquisition step by inter-frame
predictive encoding in units of frame and generating encoded data, a
wireless transmission step of wirelessly transmitting the encoded data; a
wireless transmission control step of determining a wireless state, and
when determining that the wireless sate is deteriorated, interrupting
transmission of the encoded data, and a referenced frame designation step
of, when the wireless transmission control step interrupts transmission
of the encoded data, designating a referenced frame for the inter-frame
predictive encoding in the encoding step.

[0040] Still another aspect of the present invention is an encoding method
performed in a wireless transmission terminal comprising a data
acquisition unit for acquiring data to be reproduced in time sequence, a
wireless transmission unit for encoding the data to be reproduced in time
sequence by inter-frame predictive encoding in units of frame, and
wirelessly transmitting the encoded data, and a wireless transmission
control unit for determining a wireless state of the wireless
transmission unit, and when determining that the wireless state is
deteriorated, interrupting transmission of the encoded data by the
wireless transmission unit, the encoding method comprising an encoding
step of encoding the data acquired in the data acquisition unit and
reproduced in time sequence by inter-frame predictive encoding in units
of frame and generating the encoded data, and a referenced frame
designation step of, when the wireless transmission control unit
interrupts transmission of the encoded data by the wireless transmission
unit, designating a referenced frame for the inter-frame predictive
encoding in the encoding step.

[0041] Still another aspect of the present invention is a computer program
for causing a computer to perform the wireless transmission method.

[0042] Still another aspect of the present invention is a computer program
for causing a computer to perform the encoding method.

Advantageous Effects of Invention

[0043] According to the present invention, since an inter-frame encoding
frame is generated also while transmission of encoded data by the
wireless transmission unit is being interrupted, a capacity of the buffer
required for the wireless transmission terminal can be restricted, and at
the same time, while transmission of encoded data by the wireless
transmission unit is being interrupted, a referenced frame for
inter-frame predictive encoding is designated, and thus the number of
frames which cannot be normally reproduced in a service disconnected
period can be reduced.

[0044] As described above, other aspects of the present invention are
provided. Thus, the disclosure of the present invention intends to
provide part of the present invention, and does not intend to limit the
scope of the present invention described and claimed herein.

BRIEF DESCRIPTION OF DRAWINGS

[0045] FIG. 1 is a configuration diagram of a wireless moving image
transmission terminal according to an embodiment of the present
invention.

[0046] FIG. 2 is an explanatory diagram of a moving image data
transmission processing according to the embodiment of the present
invention.

[0047] FIG. 3 is a configuration diagram of a system for wirelessly
transmitting moving image data from the wireless moving image
transmission terminal.

[0048] FIG. 4 is an explanatory diagram of a moving image data
transmission processing according to a first conventional technique.

[0049] FIG. 5 is an explanatory diagram of a case in which overflow occurs
in a buffer in the moving image data transmission processing according to
the first conventional technique.

DESCRIPTION OF EMBODIMENTS

[0050] The present invention will be described below in detail. The
embodiment of the present invention described later is merely exemplary,
and the present invention may be variously modified. Specific structures
and functions disclosed later do not intend to limit the scope of claims.

[0051] A wireless transmission terminal is directed for encoding and
wirelessly transmitting data to be reproduced in time sequence. The
wireless transmission terminal includes a data acquisition unit for
acquiring data to be reproduced in time sequence, an encoder for encoding
the data acquired in the data acquisition unit by inter-frame predictive
encoding in units of frame and generating encoded data, a wireless
transmission unit for wirelessly transmitting the encoded data, and a
wireless transmission control unit for determining a wireless state of
the wireless transmission unit, and when determining that the wireless
state is deteriorated, interrupting transmission of the encoded data by
the wireless transmission unit, and a referenced frame designation unit
for, when the wireless transmission control unit interrupts transmission
of the encoded data by the wireless transmission unit, designating a
referenced frame for inter-frame predictive encoding in the encoder.

[0052] With the structure, since not in-frame encoding frames but
inter-frame encoding frames are generated also while transmission of the
encoded data by the wireless transmission unit is being interrupted, a
small capacity of a buffer is required for storing the frames, and a
small amount of data to be transmitted is required for transmitting the
stored encoded data after wireless communication is restarted. While
transmission of the encoded data by the wireless transmission unit is
being interrupted, the referenced frame designation unit designates a
referenced frame for inter-frame predictive encoding in the encoder,
thereby avoiding a situation where a transmission destination cannot
decode a referenced frame of the encoded data transmitted after the
wireless state is recovered and the transmission of the encoded data is
restarted. The data to be reproduced in time sequence may be moving image
data, or speech data or both of them. The inter-frame predictive encoding
may be encoding including in-frame encoding frames (I pictures) and
forward predictive frames (P pictures), and encoding including
bidirectional predictive frames (B pictures).

[0053] The wireless transmission terminal may further include a buffer for
storing encoded data to be transmitted by the wireless transmission unit
while the wireless transmission control unit interrupts transmission of
the encoded data by the wireless transmission unit.

[0054] With the structure, it is possible to avoid a situation in which
the encoded data stored in the buffer cannot be decoded due to an absence
of a referenced frame at a transmission destination while the
transmission of the encoded data is interrupted.

[0055] In the wireless transmission terminal, the referenced frame
designation unit may designate, as a referenced frame, a decodable frame
among the frames transmitted before the wireless transmission control
unit interrupts transmission of the encoded data by the wireless
transmission unit.

[0056] With the structure, all the frames encoded when the referenced
frame is fixed can be decoded at the transmission destination.

[0057] In the wireless transmission terminal, the referenced frame
designation unit may designate, as a referenced frame, a decodable latest
frame among the frames transmitted before the wireless transmission
control unit interrupts transmission of the encoded data by the wireless
transmission unit.

[0058] With the structure, all the frames encoded when the referenced
frame is fixed can be decoded at the transmission destination, and the
referenced frame is made closer to the encoded frames, so that the
encoded data stored in the buffer after wireless communication is
interrupted can be decoded into higher-quality data when being decoded at
the transmission destination after the wireless communication is
restarted.

[0059] In the wireless transmission terminal, the wireless transmission
unit may transmit the encoded data stored in the buffer after the
wireless transmission control unit determines that the wireless state is
recovered.

[0060] With the structure, the encoded data encoded and stored in the
buffer after wireless communication is interrupted can be decoded at the
transmission destination after the wireless communication is restarted,
and missing data due to the interrupted wireless communication can be
reduced.

[0061] In the wireless transmission terminal, the referenced frame
designation unit may cancel designating a referenced frame after the
wireless transmission control unit determines that the wireless state is
recovered.

[0062] With the structure, after wireless communication is restarted,
normal inter-frame predictive encoding for which a referenced frame is
not fixed can be restarted, thereby efficiently compressing data.

[0063] In the wireless transmission terminal, the referenced frame
designation unit may cancel designating a referenced frame after the a
predetermined number of frames are encoded at the designated referenced
frame when the wireless transmission control unit determines that the
wireless state is recovered.

[0064] When typical inter-frame predictive encoding for which a referenced
frame is not fixed performs encoding with reference to a frame before
multiple frames, a designated referenced frame is canceled immediately
after the wireless state is recovered and wireless communication is
restarted, so that the referenced frame for the frames encoded by the
typical inter-frame predictive encoding immediately after the wireless
communication is restarted is a frame to be discarded in the buffer, and
consequently cannot be decoded. To the contrary, with the structure, a
predetermined number of frames after the wireless state is determined to
be recovered are subsequently encoded with the designated referenced
frame, thereby avoiding the disadvantage.

[0065] In the wireless transmission terminal, the buffer may discard the
stored encoded data in units of frame when receiving the encoded data
exceeding the capacity of the buffer.

[0066] With the structure, when one frame of data is divided into a
plurality of packets and is stored in the buffer in units of packet, only
part of the packets is left in the buffer and the rest of the packets is
discarded, thereby avoiding incomplete reproduction of the frames at a
transmission destination.

[0067] In the wireless transmission terminal, the buffer may discard the
stored encoded data sequentially from the oldest data.

[0068] With the structure, when encoded data exceeding the capacity of the
buffer is generated, the new encoded data can be preferentially stored
and the wireless communication is restarted to transmit the encoded data
stored in the buffer to the transmission destination, thereby reproducing
the new frames at the transmission destination.

[0069] In the wireless transmission terminal, the buffer may discard the
stored encoded data at predetermined frame intervals sequentially from
the oldest data.

[0070] With the structure, when encoded data exceeding the capacity of the
buffer is generated, the encoded data can be intermittently stored and
the wireless communication is restarted to transmit the encoded data
stored in the buffer to the transmission destination so that the data
frames can be intermittently reproduced at the transmission destination,
thereby avoiding collective time data after the wireless communication is
interrupted from missing.

[0071] In the wireless transmission terminal, the wireless transmission
unit may further include a reception function, and the wireless
transmission control unit may interrupt transmission of encoded data by
the wireless transmission unit while a reception intensity of the
wireless transmission unit is equal to or less than a predetermined
threshold.

[0072] With the structure, whether the wireless state is good can be
determined depending on the reception intensity, and until the reception
intension is recovered after the reception intensity is lowered (until
handover is completed after the handover is started, until an obstacle is
eliminated and the wireless state is recovered from the deteriorated
wireless state due to the obstacle in the wireless area, and until the
terminal returns to a wireless area after it exits the wireless area, but
not limited thereto), transmission of the encoded data is interrupted,
and the data can be encoded by inter-frame predictive encoding for which
a referenced frame is designated during the interruption.

[0073] In the wireless transmission terminal, the wireless transmission
control unit may interrupt transmission of encoded data by the wireless
transmission unit until handover is completed after the wireless
transmission terminals starts the handover.

[0074] With the structure, encoding with a designated referenced frame can
be performed in a service disconnected period due to the handover
processing, and the number of frames which cannot be retransmitted can be
reduced at the transmission destination in the service disconnected
period due to the handover processing.

[0075] Another aspect of the present invention is an encoding device used
for a wireless transmission terminal comprising a data acquisition unit
for acquiring data to be reproduced in time sequence, a wireless
transmission unit for encoding the data to be reproduced in time sequence
by inter-frame predictive encoding in units of frame and wirelessly
transmitting the encoded data, and a wireless transmission control unit
for determining a wireless state of the wireless transmission unit, and
when determining that the wireless state is deteriorated, interrupting
transmission of the encoded data by the wireless transmission unit, the
encoding device comprising an encoder for encoding the data acquired in
the data acquisition unit and reproduced in time sequence by inter-frame
predictive encoding in units of frame and generating encoded data, and a
referenced frame designation unit for, when the wireless transmission
control unit interrupts transmission of the encoded data by the wireless
transmission unit, designating a referenced frame for the inter-frame
predictive encoding in the encoder.

[0076] With the structure, while the transmission of the encoded data by
the wireless transmission unit is being interrupted, the inter-frame
encoding frames are generated so that the capacity for the encoded data
is smaller, which is advantageous for storage and transmission. While the
transmission of the encoded data by the wireless transmission unit is
being interrupted, the referenced frame designation unit designates a
referenced frame for the inter-frame predictive encoding in the encoder,
thereby avoiding a situation in which the encoded data transmitted after
the wireless state is recovered and the transmission of the encoded data
is restarted cannot be decoded due to an absence of a referenced frame at
the transmission destination.

[0077] Still another aspect of the present invention is a wireless
transmission method for encoding and wirelessly transmitting data to be
reproduced in time sequence, the wireless transmission method comprising
a data acquisition step of acquiring data to be reproduced in time
sequence, an encoding step of encoding the data acquired in the data
acquisition step by inter-frame predictive encoding in units of frame and
generating encoded data, a wireless transmission step of wirelessly
transmitting the encoded data, a wireless transmission control step of
determining a wireless state, and when determining that the wireless
state is deteriorated, interrupting transmission of the encoded data, and
a referenced frame designation step of, when transmission of the encoded
data is interrupted in the wireless transmission control step,
designating a referenced frame for the inter-frame predictive encoding in
the encoding step.

[0078] With the structure, while transmission of the encoded data is being
interrupted, inter-frame encoding frames are generated, and thus the
capacity for the encoded data is smaller, which is advantageous for
storage and transmission. When transmission of the encoded data is being
interrupted, a referenced frame for the inter-frame predictive encoding
is designated, thereby avoiding a situation in which the encoded data
transmitted after the wireless state is recovered and the transmission of
the encoded data is restarted cannot be decoded due to an absence of a
referenced frame in the transmission destination.

[0079] Still another aspect of the present invention is an encoding method
performed in a wireless transmission terminal comprising a data
acquisition unit for acquiring data to be reproduced in time sequence, a
wireless transmission unit for encoding the data to be reproduced in time
sequence by inter-frame predictive encoding in units of frame and
wirelessly transmitting the encoded data, and a wireless transmission
control unit for determining a wireless state of the wireless
transmission unit, and when determining that the wireless state is
deteriorated, interrupting transmission of the encoded data by the
wireless transmission unit, the encoding method comprising an encoding
step of encoding the data acquired in the data acquisition unit and
reproduced in time sequence by inter-frame predictive encoding in units
of frame and generating encoded data, and a referenced frame designation
step of, when the wireless transmission control unit interrupts
transmission of the encoded data by the wireless transmission unit,
designating a referenced frame for the inter-frame predictive encoding in
the encoding step.

[0080] With the structure, while transmission of the encoded data is being
interrupted, the inter-frame encoding frames are generated so that the
capacity for the encoded data is smaller, which advantages for storage
and transmission. While transmission of the encoded data is being
interrupted, a referenced frame for the inter-frame predictive encoding
is designated, thereby avoiding a situation in which the encoded data
transmitted after the wireless state is recovered and the transmission of
the encoded data is restarted cannot be decoded due to an absence of a
referenced frame in the transmission destination.

[0081] Still another aspect of the present invention is a computer program
for causing a computer to perform the wireless transmission method.

[0082] Still another aspect of the present invention is a computer program
for causing a computer to perform the encoding method.

[0083] The embodiment of the present invention will be described below
with reference to the drawings. The present invention relates to a
wireless transmission terminal for encoding and wirelessly transmitting
data to be reproduced in time sequence, but in the following embodiment,
there will be described an exemplary wireless moving image transmission
terminal in which data is moving image data and a wireless transmission
terminal wirelessly transmits moving image data. The data to be
transmitted in the wireless transmission terminal according to the
present invention may be data to be reproduced in time sequence such as
speech data, not limited to moving image data. The moving image data may
or may not include speech data.

[0084] FIG. 1 is a configuration diagram of the wireless moving image
transmission terminal according to the embodiment of the present
invention. The wireless moving image transmission terminal 100 includes a
moving image acquisition unit 1, a moving image encoding device 2, a
wireless transmission/reception unit 3, a buffer 4 and a wireless state
determination unit 5. The moving image encoding device 2 includes an
encoder 21 and a referenced frame designation unit 22.

[0085] The moving image acquisition unit 1 is a module for acquiring
moving image data, and corresponds to the data acquisition unit according
to the present invention. The moving image acquisition unit 1 according
to the present embodiment shoots an object and generates moving image
data thereby to acquire moving image data. The moving image acquisition
unit 1 may read the moving image data recorded in a recording medium
thereby to acquire the moving image data. The moving image acquisition
unit 1 outputs the acquired moving image data to the encoder 21 in the
moving image encoding device 2. The moving image data output from the
moving image acquisition unit 1 is data in units of frame. The frames are
reproduced in a time order thereby to express a moving image.

[0086] The encoder 21 encodes the moving image data output from the moving
image acquisition unit 1 by inter-frame predictive encoding. As described
in FIG. 5, in a normal time when the wireless transmission/reception unit
3 can wirelessly transmit/receive data, the encoder 21 encodes the frames
of the moving image data into encoded data including in-frame encoding
frames (I pictures) and inter-frame encoding frames (P pictures) by
inter-frame predictive encoding. That is, each inter-frame encoding frame
is generated by forward predictive encoding assuming a previous frame as
a frame to be referred to in the inter-frame predictive encoding (which
will be called "referenced frame" below). The encoder 21 outputs the
encoded data to the wireless transmission/reception unit 3.

[0087] The referenced frame designation unit 22 designates a referenced
frame for the inter-frame predictive encoding by the encoder 21 when a
predetermined condition is met. The designation of a referenced frame by
the referenced frame designation unit 22 will be described below in
detail.

[0088] The wireless transmission/reception unit 3 packetizes the encoded
data input by the encoder 21, temporarily stores the packets to be
transmitted in the buffer 4 as needed, and transmits them toward a
wireless network. The wireless transmission/reception unit 3 has a
reception function of receiving various control signals or data from the
wireless network. Access points are present (see FIG. 3) beyond the
wireless network, and the wireless moving image transmission terminal 100
transmits/receives to/from an access point in a wireless area to which
the terminal belongs.

[0089] The image acquisition unit 1 acquires the frames of a moving image
in time sequence, and sequentially outputs the same to the encoder 21.
The encoder 21 encodes the frames of the moving image input from the
image acquisition unit 1, and generates and outputs encoded data to the
wireless communication unit 3. The wireless communication unit 3
sequentially packetizes the encoded data input from the encoder 21, and
sequentially transmits the transmission packets in an order of
packetization. Thereby, a transmission destination can sequentially
decode the moving image shot by the moving image acquisition unit 1, and
real-time reproduction at the transmission destination can be realized in
this way.

[0090] The wireless state determination unit 5 performs a handover
processing of the wireless moving image transmission terminal 100. In
order to do this, the wireless state determination unit 5 determines
whether the wireless state of the wireless transmission/reception unit 3
is good. The wireless state determination unit 5 can determine whether
the wireless state is good depending on a wireless intensity received in
the wireless transmission/reception unit 3.

[0091] When the wireless intensity lowers a predetermined threshold or is
equal to or less than the predetermined threshold, the wireless state
determination unit 5 determines that the wireless state is deteriorated,
and controls the wireless transmission/reception unit 3 to interrupt the
transmission of the packets of the encoded moving image data input by the
encoder 21. When the wireless intensity is equal to or more than the
predetermined threshold or exceeds the predetermined threshold, the
wireless state determination unit 5 determines that the wireless state is
recovered, and controls the wireless transmission/reception unit 3 to
restart the transmission of the packets of the encoded moving image data
input by the encoder 21.

[0092] The situations for restarting the transmission of the packets of
the encoded moving image data include a situation in which after the
wireless state is determined to be deteriorated and handover is started,
the handover is completed and an association with a new access point is
established and a situation in which after the wireless intensity is less
than the predetermined threshold or is equal to or less than the
predetermined threshold in the wireless communication with an access
point, the wireless intensity in the wireless communication with the same
access point is equal to or more than the predetermined threshold or
exceeds the predetermined threshold.

[0093] When determining that the wireless state is deteriorated, the
wireless state determination unit 5 notifies the fact to the referenced
frame designation unit 22 in the moving image encoding device 2. When
determining that the wireless state is recovered, the wireless state
determination unit 5 notifies the fact to the referenced frame
designation unit 22 in the moving image encoding device 2.

[0094] The encoder 21 encodes the frames of the moving image data by the
inter-frame predictive encoding illustrated in FIG. 5 during a normal
time as described above. That is, the frame 1 is subjected to in-frame
encoding to be an I picture, and the frame 2 and its subsequent frames
are subjected to forward predictive encoding to be P pictures assuming a
previous frame as a referenced frame until a next in-frame encoding
frame.

[0095] When receiving a notification that the wireless state is determined
to be deteriorated from the wireless state determination unit 5, the
referenced frame designation unit 22 designates a referenced frame. When
the referenced frame designation unit 22 designates a referenced frame,
the encoder 21 does not perform normal predictive encoding as illustrated
in FIG. 6 until the designation is canceled, and fixes a referenced frame
at the designated referenced frame, and performs forward predictive
encoding.

[0096] When designating a referenced frame, the referenced frame
designation unit 22 designates, as a referenced frame, the latest frame
which is decodable by itself or by referring to the
previously-transmitted frames among the frames all the packets of which
are completely transmitted before the wireless state determination unit 5
determines that the wireless state is deteriorated and the transmission
of the packets by the wireless transmission/reception unit 3 is
interrupted. The self-decodable frames is an in-frame encoding frame (I
picture). The frame decodable by referring to the previously-transmitted
frames is a forward predictive encoding frame (P picture).

[0097] After a referenced frame is designated, the encoder 21 performs
forward predictive encoding on the frames of the moving image data
sequentially input from the moving image acquisition unit 1 to generate
encoded data with the designated referenced frame as a referenced frame.
The encoder 21 sequentially outputs the encoded data to the wireless
transmission/reception unit 3. The wireless transmission/reception unit 3
packetizes the input encoded data, but cannot transmit the packets and
thus stores the same in the buffer 4.

[0098] In this way, the wireless transmission/reception unit 3 stores the
packets in the buffer 4, and when new packets need to be stored in the
buffer 4 after the packets are stored up to the capacity of the buffer 4,
the packets of the oldest frame are discarded (erased) from the buffer 4.
At this time, the packets are discarded in units of frame, or a plurality
of packets configuring one frame is discarded at the same time.

[0099] When the wireless state determination unit 5 determines that the
wireless state is recovered and the wireless communication is restarted,
the wireless transmission/reception unit 3 transmits the packets stored
in the buffer 4 sequentially from the oldest frame. When the packets
stored in the buffer 4 are extracted and transmitted by the wireless
transmission/reception unit 3 while the wireless communication is being
interrupted, the wireless transmission/reception unit 3 sequentially
stores the encoded data input from the encoder 21 into the buffer 4.

[0100] When receiving a notification that the wireless state is recovered
from the wireless state determination unit 5, the referenced frame
designation unit 22 cancels designation of a referenced frame for the
encoder 21. After the referenced frame designation unit 22 cancels the
designation of a referenced frame, the encoder 21 performs inter-frame
predictive encoding again in the order illustrated in FIG. 6.

[0101] For the restart, the encoding may be restarted from either the I
picture or the P picture. While the wireless communication is being
interrupted, as described above, the referenced frame is fixed on the
frame before the wireless communication is interrupted, and the
referenced frame for the frame encoded by forward predictive encoding
immediately before the wireless communication is restarted is relatively
distant from the encoded frame, which can cause a deteriorated image
quality. Thus, in terms of rapid recovery of the image quality, the
in-frame encoding may be desirably performed immediately after the
wireless communication is restarted.

[0102] FIG. 2 is a diagram for explaining a moving image data transmission
processing at the wireless moving image transmission terminal 100 and a
transmission destination. The encoder 21 in the wireless moving image
transmission terminal 100 first performs in-frame encoding on the frame 1
to generate an I picture, and the wireless transmission/reception unit 3
packetizes the I picture to be transmitted. Then, the encoder 21 in the
wireless moving image transmission terminal 100 encodes the frame 2 into
a P picture, and the wireless transmission/reception unit 3 packetizes
the P picture to be transmitted.

[0103] Thereafter, when the wireless moving image transmission terminal
100 moves to an edge of the wireless area of the access point with which
it has communicated so far so that when the reception intensity is
deteriorated in the wireless transmission/reception unit 3, the wireless
state determination unit 5 determines the deteriorated reception
intensity, the transmission of the packets by the wireless
transmission/reception unit 3 is interrupted to start the handover
processing, and the referenced frame designation unit 22 designates a
referenced frame for the encoding in the encoder 21.

[0104] The encoder 21 fixes a referenced frame for subsequent encoding at
the designated referenced frame according to the designated referenced
frame. In the example of FIG. 2, the frame 2 is designated as the latest
frame or the referenced frame which is decodable by itself or by
referring to the previously-transmitted frames among the frames all the
packets of which are completely transmitted before the transmission of
the packets by the wireless transmission/reception unit 3 is interrupted.

[0105] The encoder 21 performs forward predictive encoding on the frame 3
with the designated frame 2 as a referenced frame, thereby to generate a
P picture. The wireless transmission/reception unit 3 cannot transmit the
generated P picture of the frame 3, and thus stores the packets in the
buffer 4. The encoder 21 performs forward predictive encoding also on the
frame 4 with the frame 1 as a referenced frame, thereby to generate a P
picture, and the wireless transmission/reception unit 3 stores the
packets of the frame 4 in the buffer 4.

[0106] Since the designation of the referenced frame is not canceled for
the frame 5, the encoder 21 performs forward predictive encoding with the
frame 2 as a referenced frame, thereby to generate a P picture. The
wireless transmission/reception unit 3 cannot transmit the packets of the
frame 5 and thus stores them in the buffer 4, but since the buffer 4 does
not have a free capacity for storing all the packets of the frame 5, all
the packets of the frame 3 as the oldest frame are discarded to secure a
free capacity, thereby storing the packets of the frame 5.

[0107] The handover takes several tens milliseconds to several seconds,
and a service disconnected period in which communication is interrupted
is caused during the period. The handover is completed after the packets
of the frame 5 are stored, but the packets of the frame 5 are not
transmitted when the frame 6 is packetized, and thus the packets of the
oldest frame 4 are discarded and the packets of the frame 6 are stored in
the buffer 4.

[0108] When the handover is completed, the fact is notified from the
wireless state determination unit 5 to the referenced frame designation
unit 22, and the referenced frame designation unit 22 cancels the
designation of a referenced frame for the inter-frame predictive encoding
in the encoder 21. When the handover is completed and the communication
is restarted, the wireless transmission/reception unit 3 sequentially
transmits the packets stored in the buffer 4.

[0109] When the designation of a referenced frame is canceled, the encoder
21 performs in-frame encoding on the first frame thereby to generate an I
picture.

[0110] The reception unit in the transmission destination receives the
packets transmitted from the wireless moving image transmission terminal
100. When receiving the packets of the transmission destination frame 1,
the transmission destination decodes and reproduces the packets, and when
receiving the packets of the frame 2, it decodes the frame 2 with the
frame 1 as a referenced frame. In this way, the frame 1 and the frame 2
are normally reproduced at the transmission destination.

[0111] Since the packets are not transmitted from the wireless moving
image transmission terminal 100 during handover, reproduction is
temporarily stopped at the transmission destination. When the handover
ends and the communication is restarted in the wireless moving image
transmission terminal 100, the packets of the frame 5 are first
transmitted. The frame 3 and the frame 4 are previously discarded in the
wireless moving image transmission terminal 100 and are not transmitted
to the transmission destination, and thus their frames are not reproduced
in the transmission destination.

[0112] The transmission destination decodes the frame 5 with reference to
the frame 2. The frame 6 is decoded with reference to the frame 2. If the
frame 5 is encoded with reference to the previous frame 4 as usual, the
frame 4 is discarded due to interrupted communication, and thus, even if
the frame 5 stored in the buffer during the interrupted communication is
transmitted to the transmission destination after the communication is
restarted, a referenced frame for the frame 5 is not present in the
transmission destination and cannot be decoded.

[0113] According to the present embodiment, as described above, the frames
transmitted after the communication is restarted are the frames
transmitted to the transmission destination before the communication is
interrupted, and are encoded with the decodable frame 2 as a referenced
frame, and thus the frames can be accurately decoded from the beginning
at the transmission destination after the communication is restarted.
Then, the frame 7 and its subsequent frames encoded after the designation
of the referenced frame is canceled can be decoded and reproduced as
usual.

[0114] As described above, according to the present embodiment, also when
the transmission of the encoded data by the wireless transmission unit 3
is stopped, not the in-frame encoding frames but the inter-frame encoding
frames are generated, and thus for storing the same, a small capacity of
the buffer is required, and also when the encoded data stored after the
wireless communication is restarted is transmitted, a small amount of
data to be transmitted is required. When the transmission of the encoded
data by the wireless transmission unit 3 is stopped, the referenced frame
designation unit designates a referenced frame for the inter-frame
predictive encoding in the encoder, thereby avoiding a situation in which
the encoded data transmitted after the wireless state is recovered and
the transmission of the encoded data is restarted cannot be decoded due
to an absence of a referenced frame in the transmission destination.

[0115] According to the present embodiment, the encoder 21 performs
encoding (encoding for generating I pictures and P pictures) including
only in-frame encoding and forward predictive encoding as normal
encoding, but may perform encoding (encoding for generating I pictures, P
pictures and B pictures) including in-frame encoding, forward predictive
encoding and bidirectional predictive encoding.

[0116] In the above embodiment, the wireless moving image transmission
terminal 100 has the buffer 4, and stores the frames encoded while
communication is being interrupted in the buffer 4, and transmits the
frames stored in the buffer 4 after the communication is restarted. As
the capacity is larger, the buffer 4 can store more frames acquired and
encoded while communication is being interrupted, and more frames can be
reproduced at the transmission destination after the communication is
restarted, thereby reducing missing frames.

[0117] However, the present invention is advantageous in that even when
the capacity of the buffer is not sufficient and part of the frames is
discarded while communication is being interrupted, the frames
transmitted after the communication is restarted can be immediately
decoded and reproduced. Thus, the present invention is advantageous when
the buffer does not have an enough capacity to store all the frames
generated while communication is being interrupted, and further when the
capacity of the buffer is so small or the buffer is not present.

[0118] In the present embodiment, when the capacity of the buffer is not
enough and thus part of the frames should be discarded, the frames are
sequentially discarded from the oldest frame, but the present invention
is not limited thereto. For example, the frames may be discarded at
predetermined intervals (such as only odd-numbered frames) from the
oldest frame, or the frames to be discarded may be determined by any
other method. The frames are intermittently discarded (or left) so that
after communication is restarted, not only a moving image immediately
after the restart but also former frames can be reproduced at the
transmission destination. In this way, the frames to be discarded (or
left) can be determined by any other method because a referenced frame
for the frames encoded while communication is being interrupted is fixed
on a decodable frame at the transmission destination irrespective of the
interrupted communication.

[0119] When the normal encoding is encoding with reference to a frame
before multiple frames, a referenced frame is kept designated for several
frames after communication is restarted, and the frames are encoded, and
the designated referenced frame may be then canceled such that the
inter-frame encoding frames after communication is restarted to return to
the normal encoding are not encoded with reference to the frames which
cannot be stored in the buffer to be discarded due to the interrupted
communication.

[0120] According to the embodiment, when the reception intensity in the
wireless transmission/reception unit 3 lowers the predetermined threshold
or is equal to or less than the predetermined threshold, the wireless
state determination unit 5 determines that the wireless state is
deteriorated, and interrupts transmission of the packets by the wireless
transmission/reception unit 3, and notifies the fact to the referenced
frame designation unit 22, but the present invention is not limited
thereto. When handover is started, the wireless state determination unit
5 may determine that the wireless state is deteriorated, and may notify
the fact to the referenced frame designation unit 22. The wireless state
determination unit 5 may determine that the wireless state is recovered
based on an association established with a new access point when the
handover is completed.

[0121] The preferred embodiment according to the present invention
considered so far has been described above, but the present embodiment
may be variously modified, and the scope of claims intends to encompass
all the variants within the spirit and scope of the present invention.

INDUSTRIAL APPLICABILITY

[0122] As described above, the present invention can avoid a situation in
which since a referenced frame for inter-frame predictive encoding in the
encoding is designated while transmission of encoded data is being
interrupted, a transmission destination cannot decode the encoded data
transmitted after a wireless state is recovered and the transmission of
the encoded data is restarted due to an absence of a referenced frame,
and is advantageous as a wireless transmission terminal for encoding and
wirelessly transmitting data to be reproduced in time sequence by
inter-frame predictive encoding.